P-glycoprotein (P-gP), a product of the MDRI/ABCB1 gene, was the first membrane transporter shown to confer multidrug resistance (MDR). The long-term goal of this project is to understand the mechanisms that activate MDR1 in tumor cells in response to stress agents in order to identify targets for therapeutic intervention in MDR1 activation. MDR1 is a highly stress-inducible gene and we have shown that activation in response to stress agents occurs via a transcriptional mechanism coincident with changes in chromatin. We hypothesize that MDR1 activation by stress agents involves changes in chromatin structure that are mediated by an ATP-dependent chromatin-remodeling complex. We propose to: 1.) Examine the nucleosomal structure of the MDR1 promoter by low- and high-resolution analysis of nucleosome positioning utilizing indirect end labeling and LM-PCR; 2.) Evaluate the involvement of ATP-dependent chromatin remodeling complexes MDR1 transcriptional activation by transfection analysis and Chip analysis; and 3.) Evaluate posttranslational modifications of histones at the MDR1 3romoter by transfection analysis and Western blot and Chip analysis.